TinyMCE source files can be found at github: ​https://github.com/tinymce
i don't think it is needed to include all the source files in the wordpress svn itself. as long as the external library's are used "as is" with no modifications to the source itself.

perhaps a simple solution would be to include a txt file with a link to the source code and/or website of this library?

License (update: 2010-11-11)
I get a few questions about what kind of license this player is released under. I don´t know, really.
You can do pretty much whatever the hell you want with it as far as I´m concerned ;) So use it for whatever, redistribute it, etc.
As long as you don´t try to profit from/sell it in any way, it´s probably fine. If you are unsure, just drop me a quick email.

The media plugin is buried on the second button row for single site installs and not displayed at all for multisite. It really shouldn't even be shown to those who don't have unfiltered_html. We've discussed removing it entirely in the past. Let's go ahead and lose it.